Chlorine-based hardmask removal

ABSTRACT

A method of removing titanium nitride hardmask is described. The hardmask resides above a low-k dielectric layer prior to removal and the low-k dielectric layer retains a relatively low net dielectric constant after the removal process. The low-k dielectric layer may be part of a dual damascene structure having copper at the bottom of the vias. A non-porous carbon layer is deposited prior to the titanium nitride hardmask removal to protect the low-k dielectric layer and the copper. The titanium nitride hardmask is removed with a gas-phase etch using plasma effluents formed in a remote plasma from a chlorine-containing precursor. Plasma effluents within the remote plasma are flowed into a substrate processing region where the plasma effluents react with the titanium nitride.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Prov. Pat. App. No. 62/054,913 filed Sep. 24, 2014, and titled “SELECTIVE DRY ETCH PROCESS” by Pandit et al., which is hereby incorporated herein in its entirety by reference for all purposes. This application also claims the benefit of U.S. Prov. Pat. App. No. 62/055,218 filed Sep. 25, 2014, and titled “METHOD OF TIN HARDMASK REMOVAL FOR COPPER/LOW-K DUAL DAMASCENE DEVICES” by Pandit et al., which is hereby incorporated herein in its entirety by reference for all purposes.

FIELD

Embodiments of the invention relate to removing hardmasks.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective of the first material relative to the second material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.

Dry etch processes are often desirable for selectively removing material from semiconductor substrates. The desirability stems from the ability to gently remove material from miniature structures with minimal physical disturbance. Dry etch processes also allow the etch rate to be abruptly stopped by removing the gas phase reagents. Some dry-etch processes involve the exposure of a substrate to remote plasma by-products formed from one or more precursors to achieve high etch selectivity. The high selectivities achieved enable novel process sequences.

Methods are needed to broaden the process sequences which take advantage of the high etch selectivities afforded by these novel remote plasma dry etch processes.

SUMMARY

A method of removing titanium nitride hardmask is described. The hardmask resides above a low-k dielectric layer prior to removal and the low-k dielectric layer retains a relatively low net dielectric constant after the removal process. The low-k dielectric layer may be part of a dual damascene structure having copper at the bottom of the vias. A non-porous carbon layer is deposited prior to the titanium nitride hardmask removal to protect the low-k dielectric layer and the copper. The titanium nitride hardmask is removed with a gas-phase etch using plasma effluents formed in a remote plasma from a chlorine-containing precursor. Plasma effluents within the remote plasma are flowed into a substrate processing region where the plasma effluents react with the titanium nitride.

Embodiments of the invention include methods of removing titanium nitride hardmasks. The methods include forming a carbon-containing layer over low-k dielectric walls over an underlying copper layer on a patterned substrate. The low-k dielectric walls form a gap and the patterned substrate further includes titanium nitride hardmasks above the low-k dielectric walls. One of the titanium nitride hardmasks is wider than an underlying supporting low-k dielectric wall. The methods further include etching the carbon-containing layer to expose the titanium nitride hardmasks leaving behind a remainder of the carbon-containing layer. The methods further include placing the patterned substrate in a substrate processing region of a substrate processing chamber. The methods further include flowing a chlorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents. The methods further include flowing the plasma effluents into the substrate processing region through through-holes in a showerhead disposed between the substrate processing region and the remote plasma region. The methods further include forming a local plasma in the substrate processing region to further excite the plasma effluents. The methods further include etching the titanium nitride hardmasks with the plasma effluents. The plasma effluents do not react with the underlying copper layer as a result of a presence of the remainder of the carbon-containing layer. The methods further include removing the remainder of the carbon-containing layer.

Embodiments of the invention include methods of removing titanium nitride hardmasks. The methods include forming a carbon-containing layer over low-k dielectric walls over an underlying copper layer on a patterned substrate. The low-k dielectric walls form a trench and a via fluidly coupled to one another and the low-k dielectric walls are capped with titanium nitride hardmasks. The titanium nitride hardmasks overhang the low-k dielectric walls. The methods further include dry-etching the carbon-containing layer to expose the titanium nitride hardmasks leaving behind a remainder of the carbon-containing layer. The methods further include placing the patterned substrate in a substrate processing region of a substrate processing chamber. The methods further include flowing a radical-chlorine precursor into the substrate processing region. The radical-chlorine precursor is prevented from reacting with the underlying copper layer by the remainder of the carbon-containing layer. The methods further include etching away the titanium nitride hardmasks. The methods further include removing the remainder of the carbon-containing layer.

Embodiments of the invention include methods of removing a hardmask. The methods include forming a conformal amorphous carbon-containing layer over a patterned substrate. The patterned substrate includes a trench and a via below the trench. The via is above an underlying copper layer. Sidewalls of the trench and the via include low-k dielectric walls and the sidewalls of the trench further include the hardmask comprising titanium nitride features. The titanium nitride features form a narrower gap at the top of the trench than a width of the trench between the low-k dielectric walls. The trench is fluidly coupled to the via. The methods further include etching back the conformal amorphous carbon-containing layer to expose the titanium nitride features leaving behind a remainder of the conformal amorphous carbon-containing layer. The remainder of the conformal amorphous carbon-containing layer completely covers both the underlying copper layer and the low-k dielectric walls so reactants cannot reach either the underlying copper layer or the low-k dielectric walls. The methods further include removing the titanium nitride features. The methods further include removing the remainder of the conformal amorphous carbon-containing layer.

Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed embodiments. The features and advantages of the disclosed embodiments may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodiments may be realized by reference to the remaining portions of the specification and the drawings.

FIG. 1 is a flow chart of a titanium nitride hardmask removal process according to embodiments.

FIGS. 2A, 2B, 2C, 2D and 2E show cross-sectional views of a device at stages of a titanium nitride hardmask removal process according to embodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a portion of a substrate processing chamber according to embodiments.

FIG. 3C shows a bottom view of a showerhead according to embodiments.

FIG. 4 shows a top view of an exemplary substrate processing system according to embodiments.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

A method of removing titanium nitride hardmask is described. The hardmask resides above a low-k dielectric layer prior to removal and the low-k dielectric layer retains a relatively low net dielectric constant after the removal process. The low-k dielectric layer may be part of a dual damascene structure having copper at the bottom of the vias. A non-porous carbon layer is deposited prior to the titanium nitride hardmask removal to protect the low-k dielectric layer and the copper. The titanium nitride hardmask is removed with a gas-phase etch using plasma effluents formed in a remote plasma from a chlorine-containing precursor. Plasma effluents within the remote plasma are flowed into a substrate processing region where the plasma effluents react with the titanium nitride.

Copper dual-damascene structures have been used for several decades and include two distinct patterns formed into a dielectric layer. The lower pattern may include via structures whereas the upper pattern may include a trench. The via and the trench are filled at the same time which is the operation for which the dual-damascene process gets its name. A titanium nitride hardmask may be used for one or both of the patterning operations (the via and/or the trench). The removal of the titanium nitride hardmask is accomplished herein in a manner from the methods used previously. Past methods include removing the titanium nitride hardmask using chemical mechanical polishing but the overhang of the titanium nitride hardmask has already compromised the copper filling of the via/trench. Past methods further include removing the titanium nitride using the SC1 cleaning solution prior to copper filling but the SC1 solution can damage the exposed copper at the bottom of the via. The methods presented herein avoid both of these issues.

In order to better understand and appreciate the invention, reference is now made to FIG. 1 which is a titanium nitride hardmask removal process 101 according to embodiments. Concurrently, reference will be made to FIGS. 2A, 2B, 2C, 2D and 2E which show cross-sectional views of a device at various stages of titanium nitride hardmask removal process 101. The portion of the device shown may be a back-end of the line (BEOL) interconnect portion of an integrated circuit during formation in embodiments. Prior to the first operation (FIG. 2A), an exposed titanium nitride layer is formed, patterned into titanium nitride hardmask 230, and used to pattern an underlying low-k dielectric layer 220 on the patterned substrate. Silicon carbon nitride layer 210 may be used to physically separate underlying copper layer 201 from low-k dielectric layer 220. Underlying copper layer 201 is located beneath the low-k dielectric layer and is exposed to the atmosphere through via and trench. Titanium nitride hardmask 230 may be physically separated from low-k dielectric layer 220 by an auxiliary hardmask to facilitate processing, though no such layer is shown in FIG. 2. The auxiliary hardmask layer may be a silicon oxide hardmask in embodiments. “Top”, “above” and “up” will be used herein to describe portions/directions perpendicularly distal from the substrate plane and further away from the center of mass of the substrate in the perpendicular direction. “Vertical” will be used to describe items aligned in the “up” direction towards the “top”. Other similar terms may be used whose meanings will now be clear.

A carbon-containing layer 240-1 is formed on the patterned substrate in operation 110, shown following formation in FIG. 2B. The carbon-containing layer may be nonconformal or conformal on the features of patterned substrate in embodiments. The carbon-containing layer may mostly fill gaps or completely fill gaps (as shown in FIG. 2B) in the low-k dielectric layer of the patterned substrate including the via and/or the trench in the example of FIGS. 1-2. Carbon-containing layer 240-1 may be an amorphous carbon gapfill carbon-containing layer 240-1 having a higher density and lower porosity than, for example, organic carbon-containing layers in embodiments. The carbon-containing layer may inhibit diffusion of subsequently-introduced etchants and may therefore protect the integrity of low-k dielectric layer 220 and underlying copper layer 201 during processing. A silicon carbon nitride layer 210 may be positioned between underlying copper layer 201 and low-k dielectric layer 220 as shown in FIG. 2A. Organic carbon-containing layers have been found to allow diffusion of etchants which increase the effective dielectric constant of low-k dielectric layer 220 and corrode underlying copper layer 201. Organic carbon-containing layers, such as organic planarization layers, retain chemical bonding geometries present in organic molecules and therefore allow diffusion when carbon-containing layer 240-1 inhibits or stops diffusion in embodiments. The carbon-containing layer may comprise or consist only of carbon, hydrogen and nitrogen in embodiments.

Carbon-containing layer 240-1 is etched back to expose titanium nitride hardmask 230 in operation 120, shown following the operation in FIG. 2C. Etching operation 120 may be anisotropic or isotropic according to embodiments. Etching operation 120 may involve remote and/or locally excited etchants formed from halogen-containing and/or oxygen-containing precursors. Oxygen-containing precursors may be used to etch back carbon-containing layer 240-1, however, enough carbon-containing layer 240-2 should be retained to completely seal low-k dielectric layer 220 in embodiments. Sealing low-k dielectric layer 220 with carbon-containing layer 240-2 avoids any excessive increase in dielectric constant for low-k dielectric layer 220 in subsequent processing. Halogen-containing precursors may be used to etch back carbon-containing layer 240-1, according to embodiments, and the plasmas (local and/or remote) may be devoid of oxygen during operation 120.

A flow of chlorine (Cl₂) is introduced into a plasma region separate from the processing region (operation 130). Other sources of chlorine may be used to augment or replace the chlorine. In general, a chlorine-containing precursor may be flowed into the plasma region, such as diatomic chlorine (Cl₂), atomic chlorine, xenon dichloride or boron trichloride. The separate plasma region may be referred to as a remote plasma region herein and may be within a distinct module from the processing chamber or a compartment within the processing chamber. A carbon-and-hydrogen-containing precursor, such as methane, may also be flowed into the plasma region excited along with the chlorine. The carbon-and-hydrogen-containing precursor is optional and included primarily to help remove titanium oxide which is often present as a thin oxidation layer on the surface of the titanium nitride.

The plasma effluents formed in the remote plasma region are flowed into the substrate processing region (in operation 130 as well). Titanium nitride hardmask 230 on the substrate is selectively etched (operation 140) such that titanium nitride hardmask 230 may be removed more rapidly than a variety of other materials. FIG. 2D shows the patterned substrate following operation 140. Operation 140 may involve removal or complete removal of the titanium nitride hardmasks in embodiments. The selective etch of all examples disclosed herein may etch titanium nitride significantly faster than a variety of titanium-free dielectric materials which may include hafnium oxide (HfO₂) or a silicon-containing material such as silicon (e.g. polysilicon), silicon oxide, low-K dielectric, silicon nitride or silicon carbon nitride according embodiments. Such a process may have broad-based utility, for example, the etch processes disclosed herein may be used to selectively remove titanium nitride from atop a silicon-containing film stack after patterning. Carbon-containing layer 240-1 may be removed at this point (in operation 150) since the protection afforded by carbon-containing layer 240-1 may no longer be necessary at this point in the process. FIG. 2E shows the patterned substrate following operation 150.

The titanium nitride etch selectivity of the processes disclosed herein may be greater than or about 10:1, greater than or about 20:1, greater than or about 50:1, or greater than or about 100:1 for materials other than titanium nitride in embodiments. Applying a bias power, but keeping the level low as recited shortly, may increase these already-elevated selectivities. The processes disclosed herein display etch selectivities of titanium nitride relative to a variety of specific materials. In practice, under conditions of low bias power in the substrate processing region local plasma, etch rates of many of these materials were so low as to be not accurately measurable. The etch selectivity of titanium nitride relative to silicon oxide may be greater than or about 100:1, greater than or about 250:1, greater than or about 500:1 or greater than or about 1000:1 in embodiments. Silicon oxide may be used as a hardmask layer between low-k dielectric layer 220 and titanium nitride hardmask 230. Low-k dielectric films and silicon carbon nitride films, such as Black Diamond III™ and Blok™ (both available from Applied Materials), respectively, displayed essentially unmeasurable etch rates. The etch selectivity of titanium nitride relative to silicon oxycarbide (e.g. Black Diamond III™) may be greater than or about 100:1, greater than or about 250:1, greater than or about 500:1 or greater than or about 1000:1 in embodiments. The etch selectivity of titanium nitride relative to silicon carbon nitride (e.g. Blok™) may be greater than or about 100:1, greater than or about 250:1, greater than or about 500:1 or greater than or about 1000:1 according to embodiments.

The trench structures filled with the carbon-containing layer may be a dual-damascene structure including a via underlying a trench. The via may be a low aspect ratio gap and may be, e.g., circular as viewed from above the patterned substrate laying flat. The structure may be at the back end of the line which may result in larger dimensions depending on the device type. A width of the via may be less than 50 nm, less than 40 nm, less than 30 nm or less than 20 nm according to embodiments. A width of the trench may be less than 70 nm, less than 50 nm, less than 40 nm or less than 30 nm in embodiments. The dimensions described herein apply to a dual-damascene structure or structures involving a single layer. An aspect ratio of the via may be about 1:1, as viewed from above, whereas an aspect ratio of the trench may be greater than 10:1 since the trench is used to contain a conductor meant to electrically attach multiple vias.

The carbon-and-hydrogen-containing precursor is included primarily to help remove the titanium oxide layer from atop the titanium nitride layer. The carbon-and-hydrogen-containing precursor may be methane (CH₄) as in the example, but may also be a higher order hydrocarbon such as ethane (C₂H₆). In general, the carbon-and-hydrogen-containing precursor may include carbon and hydrogen and may consist only of carbon and hydrogen. The carbon-and-hydrogen-containing precursor may contain only single bonds in embodiments. A hydrocarbon with some multiple bonds may be used and hydrogen (H₂) may be added to the remote plasma region as well, during the process, in order to adjust the H:C atomic flow ratio.

The flows of the chlorine-containing precursor and optional carbon-and-hydrogen-containing precursor may further include one or more relatively inert gases such as He, N₂, Ar. The inert gas can be used to improve plasma stability or process uniformity. Argon is helpful, as an additive, to promote the formation of a stable plasma. Process uniformity is generally increased when helium is included. These additives are present in embodiments throughout this specification. Flow rates and ratios of the different gases may be used to control etch rates and etch selectivity.

In embodiments, the chlorine-containing precursor (e.g. Cl₂) is supplied at a flow rate of between about 25 sccm (standard cubic centimeters per minute) and 800 sccm, the carbon-and-hydrogen-containing precursor (e.g. CH₄) at a flow rate of between about 50 sccm and 600 sccm, He at a flow rate of between about 0 slm (standard liters per minute) and 3 slm, and Ar at a flow rate of between about 0 slm and 3 slm. One of ordinary skill in the art would recognize that other gases and/or flows may be used depending on a number of factors including processing chamber configuration, substrate size, geometry and layout of features being etched.

During etching process 140, the substrate may be maintained may be between about −30° C. and about 400° C. in general. The temperature of the patterned substrate during etching operation 140 may be between −20° C. and 350° C., −10° C. and −250° C., between 0° C. and 50° C. or between 5° C. and 20° C. in embodiments. The pressure in the substrate processing region and the remote plasma region(s) during etching operation 140 may be between 0.1 Torr and 50 Torr, between 1 Torr and 15 Torr or between 5 Torr and 10 Torr in embodiments. By maintaining the substrate temperature relatively low, such as below 10° C., and maintaining the process chamber at a pressure below 10 Torr, the etch selectivity may be enhanced through the suppression of the etch rate of the materials other than titanium nitride.

The method also includes applying energy to the chlorine-containing precursor and the optional carbon-and-hydrogen-containing precursor (CH₄) while they are in the remote plasma region to generate the plasma effluents. As would be appreciated by one of ordinary skill in the art, the plasma may include a number of charged and neutral species including radicals and ions. The plasma in the remote plasma region (e.g. in the chamber plasma region) may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power, inductively coupled power, etc.). In an embodiment, the energy is applied using a capacitively-coupled plasma unit. The remote plasma source power may be between about 40 watts and about 1500 watts, between about 100 watts and about 1200 watts, between about 250 watts and about 1000 watts, or between about 400 watts and about 800 watts in embodiments. The 400 watt to 800 watt range may optimize the selective removal of titanium nitride relative to a variety of other exposed materials including silicon-containing dielectric films as well as some metals and metal oxides which do not contain titanium. The capacitively-coupled plasma unit may be disposed remote from the substrate processing region but still within the substrate processing chamber. For example, the capacitively-coupled plasma unit and the plasma generation region may be separated from the gas reaction region by a showerhead. Alternatively, The remote plasma power may be applied to the remote plasma region at a level between 500 W and 10 kW for a remote plasma external to the substrate processing chamber. The remote plasma power may be applied using inductive coils, in embodiments, in which case the remote plasma will be referred to as an inductively-coupled plasma (ICP).

Plasma power may also be simultaneously applied to both the remote plasma region (e.g. the chamber plasma region) and substrate processing region during etching processes described herein. The plasma in the chamber plasma region may have a higher power applied in order to create a high concentration of neutral radicals entering substrate processing region. The plasma power applied to substrate processing region may be lower in order to not unduly increase the ionic concentration near the substrate. However, the local plasma in the substrate processing region may be biased relative to the substrate in order to apply a sputtering component. A sputtering component of the local plasma may be included primarily to remove titanium oxide which may cover the titanium nitride to be etched. The plasma in the substrate processing region may be referred to herein as a local plasma because it resides nearest the substrate and within the substrate processing region. The local plasma may be generated using the same techniques used to create the remote plasma. As with the remote plasma, the energy may be applied using a capacitively-coupled plasma unit by applying RF power between plates above and below the substrate during etching. The local plasma RF power may be between about 5 watts and about 200 watts, between about 10 watts and about 150 watts, between about 15 watts and about 100 watts, or between about 20 watts and about 80 watts in embodiments. The lower local RF power of the local plasma in the substrate processing region keeps the ionic concentration down so the etch selectivity toward titanium nitride remains high. The local plasma RF power may be less than or about 20% of the remote plasma RF power, less than or about 15% of the remote plasma RF power, or less than or about 10% of the remote plasma RF power.

The local plasma is used, in embodiments, to facilitate removal of a titanium oxide layer which may be on top of the titanium nitride layer. The local plasma may be biased relative to the substrate to further assist removal of any titanium oxide layer by using a physical sputtering mechanism in addition to the chemical mechanism. Titanium oxide may require the sputtering assistance because the bonding is stronger in titanium oxide than in titanium nitride. The local plasma bias RF power may be between about 2 watts and about 100 watts, between about 3 watts and about 75 watts, between about 5 watts and about 60 watts, or between about 10 watts and about 50 watts in embodiments. The local plasma bias RF power is not included in the local plasma RF power so the total applied RF power is the sum of these two quantities.

Despite the optional use of local plasma excitation, an ion suppressor (which may be the showerhead) may be used to provide radical and/or neutral species for gas-phase etching. The ion suppressor may also be referred to as an ion suppression element. In embodiments, for example, the ion suppressor is used to filter etching plasma effluents en route from the remote plasma region to the substrate processing region. The ion suppressor may be used to provide a reactive gas having a higher concentration of radicals than ions. Plasma effluents pass through the ion suppressor disposed between the remote plasma region and the substrate processing region. The ion suppressor functions to dramatically reduce or substantially eliminate ionic species traveling from the plasma generation region to the substrate. The ion suppressors described herein are simply one way to achieve a low electron temperature in the substrate processing region during the gas-phase etch processes described herein.

In embodiments, an electron beam is passed through the substrate processing region in a plane parallel to the substrate to reduce the electron temperature of the plasma effluents. A simpler showerhead may be used if an electron beam is applied in this manner. The electron beam may be passed as a laminar sheet disposed above the substrate in embodiments. The electron beam provides a source of neutralizing negative charge and provides a more active means for reducing the flow of positively charged ions towards the substrate and increasing the etch selectivity in embodiments. The flow of plasma effluents and various parameters governing the operation of the electron beam may be adjusted to lower the electron temperature measured in the substrate processing region.

The electron temperature may be measured using a Langmuir probe in the substrate processing region during excitation of a plasma in the remote plasma. In aluminum removal embodiments, the electron temperature may be less than 0.5 eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV. These extremely low values for the electron temperature are enabled by the presence of the electron beam, showerhead and/or the ion suppressor. Uncharged neutral and radical species may pass through the electron beam and/or the openings in the ion suppressor to react at the substrate. Such a process using radicals and other neutral species can reduce plasma damage compared to conventional plasma etch processes that include sputtering and bombardment. Embodiments of the present invention are also advantageous over conventional wet etch processes where surface tension of liquids can cause bending and peeling of small features. In point of contrast, the electron temperature during the aluminum oxide removal process may be greater than 0.5 eV, greater than 0.6 eV or greater than 0.7 eV according to embodiments.

The substrate processing region may be described herein as “plasma-free” during the etch processes described herein. “Plasma-free” does not necessarily mean the region is devoid of plasma. Ionized species and free electrons created within the plasma region may travel through pores (apertures) in the partition (showerhead) at exceedingly small concentrations. The borders of the plasma in the chamber plasma region may encroach to some small degree upon the substrate processing region through the apertures in the showerhead. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the etch processes described herein. All causes for a plasma having much lower intensity ion density than the chamber plasma region during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein.

The examples described herein involve the preparation of a long trench above a low-aspect ratio via in a dual-damascene structure. Generally speaking the structure may involve only one level and the low-k dielectric layer may have a long trench and/or a low-aspect ratio via according to embodiments. For the purposes of description herein and claim recitations below, a via is simply a low-aspect ratio trench and so the term “trench” covers all holes in a low-k dielectric described herein. The use of carbon-containing layer 240 avoids the requirement of leaving a portion of silicon carbon nitride layer 210 at the bottom of the trench to protect underlying copper layer 201. A low-temperature oxide (LTO) was used instead of carbon-containing layer 240 and the low-k structures distorted and collapsed. Using carbon-containing layer 240 to protect low-k dielectric layer 220 and underlying copper layer 201 may avoid distorting and ruining low-k structures according to embodiments. Generally speaking, underlying copper layer 201 may be any underlying conducting layer in embodiments. Following operation 150, the trench and the via may be filled with a conductor (e.g. copper) to complete the dual-damascene portion of a semiconductor manufacturing process.

FIG. 3A shows a cross-sectional view of an exemplary substrate processing chamber 1001 with a partitioned plasma generation region within the processing chamber. During film etching, a process gas may be flowed into chamber plasma region 1015 through a gas inlet assembly 1005. A remote plasma system (RPS) 1002 may optionally be included in the system, and may process a first gas which then travels through gas inlet assembly 1005. The process gas may be excited within RPS 1002 prior to entering chamber plasma region 1015. Accordingly, the chlorine-containing precursor as discussed above, for example, may pass through RPS 1002 or bypass the RPS unit in embodiments.

A cooling plate 1003, faceplate 1017, ion suppressor 1023, showerhead 1025, and a substrate support 1065 (also known as a pedestal), having a substrate 1055 disposed thereon, are shown and may each be included according to embodiments. Pedestal 1065 may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration may allow the substrate 1055 temperature to be cooled or heated to maintain relatively low temperatures, such as between −20° C. to 200° C. Pedestal 1065 may also be resistively heated to relatively high temperatures, such as between 100° C. and 1100° C., using an embedded heater element.

Exemplary configurations may include having the gas inlet assembly 1005 open into a gas supply region 1058 partitioned from the chamber plasma region 1015 by faceplate 1017 so that the gases/species flow through the holes in the faceplate 1017 into the chamber plasma region 1015. Structural and operational features may be selected to prevent significant backflow of plasma from the chamber plasma region 1015 back into the supply region 1058, gas inlet assembly 1005, and fluid supply system 1010. The structural features may include the selection of dimensions and cross-sectional geometries of the apertures in faceplate 1017 to deactivate back-streaming plasma. The operational features may include maintaining a pressure difference between the gas supply region 1058 and chamber plasma region 1015 that maintains a unidirectional flow of plasma through the showerhead 1025. The faceplate 1017, or a conductive top portion of the chamber, and showerhead 1025 are shown with an insulating ring 1020 located between the features, which allows an AC potential to be applied to the faceplate 1017 relative to showerhead 1025 and/or ion suppressor 1023. The insulating ring 1020 may be positioned between the faceplate 1017 and the showerhead 1025 and/or ion suppressor 1023 enabling a capacitively coupled plasma (CCP) to be formed in the chamber plasma region.

The plurality of holes in the ion suppressor 1023 may be configured to control the passage of the activated gas, i.e., the ionic, radical, and/or neutral species, through the ion suppressor 1023. For example, the aspect ratio of the holes, or the hole diameter to length, and/or the geometry of the holes may be controlled so that the flow of ionically-charged species in the activated gas passing through the ion suppressor 1023 is reduced. The holes in the ion suppressor 1023 may include a tapered portion that faces chamber plasma region 1015, and a cylindrical portion that faces the showerhead 1025. The cylindrical portion may be shaped and dimensioned to control the flow of ionic species passing to the showerhead 1025. An adjustable electrical bias may also be applied to the ion suppressor 1023 as an additional means to control the flow of ionic species through the suppressor. The ion suppression element 1023 may function to reduce or eliminate the amount of ionically charged species traveling from the plasma generation region to the substrate. Uncharged neutral and radical species may still pass through the openings in the ion suppressor to react with the substrate.

Plasma power can be of a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma may be provided by RF power delivered to faceplate 1017 relative to ion suppressor 1023 and/or showerhead 1025. The RF power may be between about 10 watts and about 5000 watts, between about 100 watts and about 2000 watts, between about 200 watts and about 1500 watts, or between about 200 watts and about 1000 watts in embodiments. The RF frequency applied in the exemplary processing system may be low RF frequencies less than about 200 kHz, high RF frequencies between about 10 MHz and about 15 MHz, or microwave frequencies greater than or about 1 GHz in embodiments. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the remote plasma region.

A precursor, for example a chlorine-containing precursor and a carbon-and-hydrogen-containing precursor, may be flowed into substrate processing region 1033 by embodiments of the showerhead described herein. Excited species derived from the process gas in chamber plasma region 1015 may travel through apertures in the ion suppressor 1023, and/or showerhead 1025 and react with an additional precursor flowing into substrate processing region 1033 from a separate portion of the showerhead. Alternatively, if all precursor species are being excited in chamber plasma region 1015, no additional precursors may be flowed through the separate portion of the showerhead. Little or no plasma may be present in substrate processing region 1033 during the remote plasma etch process. Excited derivatives of the precursors may combine in the region above the substrate and/or on the substrate to etch structures or remove species from the substrate.

The processing gases may be excited in chamber plasma region 1015 and may be passed through the showerhead 1025 to substrate processing region 1033 in the excited state. A local plasma may be formed in substrate processing region 1033 concurrently with the remote plasma in the chamber plasma region 1015 as described previously. Alternatively, a plasma may not be generated in substrate processing region 1033 in embodiments.

FIG. 3B shows a detailed view of the features affecting the processing gas distribution through faceplate 1017. The gas distribution assemblies such as showerhead 1025 for use in the processing chamber section 1001 may be referred to as dual channel showerheads (DCSH) and are additionally detailed in the embodiments described in FIG. 3A as well as FIG. 3C herein. The dual channel showerhead may provide for etching processes that allow for separation of etchants outside of the processing region 1033 to provide limited interaction with chamber components and each other prior to being delivered into the processing region.

The showerhead 1025 may comprise an upper plate 1014 and a lower plate 1016. The plates may be coupled with one another to define a volume 1018 between the plates. The coupling of the plates may be so as to provide first fluid channels 1019 through the upper and lower plates, and second fluid channels 1021 through the lower plate 1016. The formed channels may be configured to provide fluid access from the volume 1018 through the lower plate 1016 by way of second fluid channels 1021 alone, and the first fluid channels 1019 may be fluidly isolated from the volume 1018 between the plates and the second fluid channels 1021. The volume 1018 may be fluidly accessible through a side of the gas distribution assembly 1025. Although the exemplary system of FIGS. 3A-3C includes a dual-channel showerhead, it is understood that alternative distribution assemblies may be utilized that maintain first and second precursors fluidly isolated prior to substrate processing region 1033. For example, a perforated plate and tubes underneath the plate may be utilized, although other configurations may operate with reduced efficiency or not provide as uniform processing as the dual-channel showerhead described.

In the embodiment shown, showerhead 1025 may distribute by way of first fluid channels 1019 process gases which contain plasma effluents upon excitation by a plasma in chamber plasma region 1015. In embodiments, the process gas introduced into RPS 1002 and/or chamber plasma region 1015 may contain chlorine, e.g., Cl₂ and possibly a carbon-and-hydrogen-containing precursor such as CH₄. The process gas may also include a carrier gas such as helium, argon, nitrogen (N₂), etc. Plasma effluents may include ionized or neutral derivatives of the process gas and may also be referred to herein as a radical-chlorine precursor referring to the atomic constituent of the process gas introduced.

FIG. 3C is a bottom view of a showerhead 1025 for use with a processing chamber in embodiments. Showerhead 1025 corresponds with the showerhead shown in FIG. 3A. Through-holes 1031, which show a view of first fluid channels 1019, may have a plurality of shapes and configurations to control and affect the flow of precursors through the showerhead 1025. Small holes 1027, which show a view of second fluid channels 1021, may be distributed substantially evenly over the surface of the showerhead, even amongst the through-holes 1031, which may help to provide more even mixing of the precursors as they exit the showerhead than other configurations.

Embodiments of the dry etch systems may be incorporated into larger fabrication systems for producing integrated circuit chips. FIG. 4 shows one such processing system (mainframe) 1101 of deposition, etching, baking, and curing chambers in embodiments. In the figure, a pair of front opening unified pods (load lock chambers 1102) supply substrates of a variety of sizes that are received by robotic arms 1104 and placed into a low pressure holding area 1106 before being placed into one of the substrate processing chambers 1108 a-f. A second robotic arm 1110 may be used to transport the substrate wafers from the holding area 1106 to the substrate processing chambers 1108 a-f and back. Each substrate processing chamber 1108 a-f, can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation, and other substrate processes.

The showerhead may be referred to as a dual-channel showerhead as a result of the two distinct pathways into the substrate processing region. The chlorine-containing precursor and the carbon-and-hydrogen-containing precursor may be flowed through the through-holes in the dual-zone showerhead and auxiliary precursors may pass through separate zones in the dual-zone showerhead. The separate zones may open into the substrate processing region but not into the remote plasma region as described above.

Combined flow rates of water vapor and plasma effluents into the substrate processing region may account for 0.05% to about 20% by volume of the overall gas mixture; the remainder being carrier gases. The chlorine-containing precursor and the carbon-and-hydrogen-containing precursor flowed into the remote plasma region but the plasma effluents has the same volumetric flow ratio, in embodiments. In the case of the chlorine-containing precursor, a purge or carrier gas may be first initiated into the remote plasma region before those of the chlorine-containing gas and the carbon-and-hydrogen-containing precursor to stabilize the pressure within the remote plasma region.

As used herein “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂ but may include concentrations of other elemental constituents such as, e.g., nitrogen, hydrogen and carbon. In some embodiments, silicon oxide portions etched using the methods disclosed herein consist essentially of silicon and oxygen. Exposed “silicon nitride” of the patterned substrate is predominantly Si₃N₄ but may include concentrations of other elemental constituents such as, e.g., oxygen, hydrogen and carbon. In some embodiments, silicon nitride portions described herein consist essentially of silicon and nitrogen. Exposed “titanium nitride” of the patterned substrate is predominantly titanium and nitrogen but may include concentrations of other elemental constituents such as, e.g., oxygen, hydrogen and carbon. In some embodiments, titanium nitride portions described herein consist essentially of titanium and nitrogen. The amorphous carbon-containing film may include about 79% carbon, 20% hydrogen and 1% nitrogen or may contain 75-83% carbon, 18%-22% hydrogen and 0.3-2% hydrogen in embodiments. “Copper” of the patterned substrate is predominantly copper but may include concentrations of other elemental constituents such as, e.g., oxygen, hydrogen and carbon. In some embodiments, copper portions described herein consist essentially of copper.

The terms “gap” and “trench” are used throughout with no implication that the etched geometry has a large horizontal aspect ratio. Viewed from above the surface, trenches may appear circular, oval, polygonal, rectangular, or a variety of other shapes. A trench may be in the shape of a moat around an island of material. The term “via” is used to refer to a low aspect ratio trench (as viewed from above) which may or may not be filled with metal to form a vertical electrical connection. As used herein, a conformal etch process refers to a generally uniform removal of material on a surface in the same shape as the surface, i.e., the surface of the etched layer and the pre-etch surface are generally parallel. A person having ordinary skill in the art will recognize that the etched interface likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.

The term “precursor” is used to refer to any process gas which takes part in a reaction to either remove material from or deposit material onto a surface. “Plasma effluents” describe gas exiting from the chamber plasma region and entering the substrate processing region. Plasma effluents are in an “excited state” wherein at least some of the gas molecules are in vibrationally-excited, dissociated and/or ionized states. A “radical precursor” is used to describe plasma effluents (a gas in an excited state which is exiting a plasma) which participate in a reaction to either remove material from or deposit material on a surface. “Radical-chlorine precursors” describe radical precursors which contain chlorine but may contain other elemental constituents. “Radical-carbon-hydrogen precursors” describe radical precursors which contain carbon and hydrogen but may contain other elemental constituents. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated into a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film.

Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups. 

The invention claimed is:
 1. A method of removing titanium nitride hardmasks, the method comprising: forming a carbon-containing layer over low-k dielectric walls over an underlying copper layer on a patterned substrate, wherein the low-k dielectric walls form a gap and the patterned substrate further comprises titanium nitride hardmasks above the low-k dielectric walls, wherein one of the titanium nitride hardmasks is wider than an underlying supporting low-k dielectric wall and the carbon-containing layer completely fills the gap; etching the carbon-containing layer to expose the titanium nitride hardmasks leaving behind a remainder of the carbon-containing layer; placing the patterned substrate in a substrate processing region of a substrate processing chamber; flowing a chlorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents; flowing the plasma effluents into the substrate processing region through through-holes in a showerhead disposed between the substrate processing region and the remote plasma region; forming a local plasma in the substrate processing region to further excite the plasma effluents; etching the titanium nitride hardmasks with the plasma effluents, wherein the plasma effluents do not react with the underlying copper layer as a result of a presence of the remainder of the carbon-containing layer; and removing the remainder of the carbon-containing layer.
 2. The method of claim 1 wherein the operation of etching the titanium nitride hardmasks removes the titanium nitride hardmasks.
 3. The method of claim 1 wherein the operation of flowing the chlorine-containing precursor further comprises flowing a carbon-and-hydrogen-containing precursor into the remote plasma region.
 4. The method of claim 1 wherein the chlorine-containing precursor comprises a precursor selected from the group consisting of atomic chlorine, diatomic chlorine, boron trichloride, and xenon dichloride.
 5. A method of removing titanium nitride hardmasks, the method comprising: forming a carbon-containing layer over low-k dielectric walls over an underlying copper layer on a patterned substrate, wherein the low-k dielectric walls form a trench and a via fluidly coupled to one another and the low-k dielectric walls are capped with titanium nitride hardmasks, wherein the titanium nitride hardmasks overhang the low-k dielectric walls and the carbon-containing layer completely fills the via and the trench; dry-etching the carbon-containing layer to expose the titanium nitride hardmasks leaving behind a remainder of the carbon-containing layer; placing the patterned substrate in a substrate processing region of a substrate processing chamber; flowing a radical-chlorine precursor into the substrate processing region, wherein the radical-chlorine precursor is prevented from reacting with the underlying copper layer by the remainder of the carbon-containing layer; etching away the titanium nitride hardmasks; and removing the remainder of the carbon-containing layer.
 6. The method of claim 5 wherein a width of the via is less than 50 nm.
 7. The method of claim 5 wherein a width of the trench is less than 70 nm.
 8. The method of claim 5 further comprising an operation of filling the via and the trench with copper after the operation of removing the remainder of the carbon-containing layer.
 9. The method of claim 5 wherein an electron temperature within the substrate processing region is below 0.5 eV during the operation of etching away the titanium nitride hardmasks.
 10. The method of claim 5 wherein a silicon carbon nitride layer is disposed between the underlying copper layer and at least one of the low-k dielectric walls.
 11. The method of claim 5 wherein the radical-chlorine precursor is prevented from reacting with the low-k dielectric walls by the remainder of the carbon-containing layer.
 12. The method of claim 5 wherein the carbon-containing layer consists only of carbon, hydrogen and nitrogen.
 13. A method of removing a hardmask, the method comprising: forming a conformal amorphous carbon-containing layer over a patterned substrate, wherein the patterned substrate comprises a trench and a via below the trench, wherein the via is above an underlying copper layer, wherein sidewalls of the trench and the via comprise low-k dielectric walls and the sidewalls of the trench further comprise the hardmask comprising titanium nitride features, wherein the titanium nitride features form a narrower gap at the top of the trench than a width of the trench between the low-k dielectric walls, and wherein the trench is fluidly coupled to the via and the conformal amorphous carbon-containing layer completely fills the via and the trench; etching back the conformal amorphous carbon-containing layer to expose the titanium nitride features leaving behind a remainder of the conformal amorphous carbon-containing layer, wherein the remainder of the conformal amorphous carbon-containing layer completely covers both the underlying copper layer and the low-k dielectric walls so reactants cannot reach either the underlying copper layer or the low-k dielectric walls; removing the titanium nitride features; and removing the remainder of the conformal amorphous carbon-containing layer.
 14. The method of claim 13 wherein the hardmask further comprises silicon oxide features underlying the titanium nitride features and overlying the low-k dielectric walls. 